Concentration dependence of water self-diffusion coefficients in dilute glycerol–water binary and glycerol–water–sodium chloride ternary solutions and the insights from hydrogen bonds

Water self-diffusion coefficients for glycerol–water binary and glycerol–water–sodium chloride ternary solutions at low glucose concentrations have been predicted using the mean square displacements method. It was found that the water self-diffusion coefficient decreases as the glycerol concentration increases. The reasons for the decrease have been analysed from the viewpoint of the hydrogen bonds.     

低密度Ar熔化及结晶的分子动力学模拟

采用有位移力的ＬｅｎｎａｒｄＪｏｎｅｓ（１２－６）势对微正则系综下低密度Ａｒ系统（简约数密度为ρ＝０．８５）的一级相变过程进行了细致的分子动力学模拟,发现Ａｒ系统的熔化过程是原子的崩塌过程,结晶过程和理想的完整晶体不同,是一活化过程：形核长大过程随温度的降低进行,原来均匀分布在系统中的自由体积呈集中分布,由此系统达到了更稳定的结晶状态。     

Molecular dynamics of MgSiO3 perovskite melting

The melting curve of MgSiO分子动力学 MgSiO3钙钛矿 熔化温度 高压melting temperature, molecular dynamics, high pressureProject supported by the National Natural Science Foundation of China (Grant Nos 10274055 and 10376021),the Natural Science Foundation of Gansu Province, China (Grant No 3ZS051-A25-027) and the Scientific Research Foundation of Education Bureau of Gansu Province, China (Grant No 0410-01).2005-01-125/8/2005 12:00:00 AMThe melting curve of MgSiO3 perovskite is simulated using molecular dynamics simulations method at high pressure. It is shown that the simulated equation of state of MgSiO3 perovskite is very successful in reproducing accurately the experimental data. The pressure dependence of the simulated melting temperature of MgSiO3 perovskite reproduces the stability of the orthorhombic perovskite phase up to high pressure of 130GPa at ambient temperature, consistent with the theoretical data of the other calculations. It is shown that its transformation to the cubic phase and melting at high pressure and high temperature are in agreement with recent experiments.     

自由能方法与零压下Al的熔化温度

利用自由能方法的分子动力学模拟,计算了零压下Al的熔化温度.在计算液相自由能的过程中,采用勒纳-琼斯(LJ)液体作为参考系统,同时将计算结果与Mei和Davenport等人的计算结果进行了比较,计算结果表明：1)选用LJ参考系统使液相自由能的计算时间节省一半,并且不影响熔化温度的计算结果;2)采用不同的埋入原子势(EAM)的分子动力学模拟计算得到的熔化温度与实验值都存在偏差,而就金属Al而言,采用Cai等人的EAM势的熔化温度的计算结果比Mei和Davenport及Morris等人采用的势模型的结果略有改关键词：熔化温度自由能方法分子动力学模拟     

分子动力学模拟Cu(010)基体对负载Co-Cu双金属团簇熔化过程的影响

纳米团簇负载到基体上的结构演化和热稳定性是其走向技术应用的关键. 本文用分子动力学结合嵌入原子方法模拟了具有二十面体初始结构的Co₂₈₁Cu₂₈₀ 混合双金属团簇在Cu(010)基体上的熔化过程, 考察了基体的Cu原子可以自由移动(自由基体)和固定(固定基体)两种条件对负载团簇熔化的影响. 发现基体条件对团簇的熔化有明显的影响. 在自由基体上团簇原子的温度-能量曲线存在明显的团簇熔化时的能量突变点, 熔点为1320 K, 低于固定基体上团簇的熔点1630 K. 在升温过程中团簇的二十面体结构会在基体表面发生外延生长. 外延团簇随着温度增加发生表面预熔, 预熔原子会逐渐向基体表面扩散形成薄层, 直至完全熔化. 自由基体上团簇原子的嵌入行为会使原子的分布状态产生不同于固定基体上的演变.     

Molecular dynamics study for the melting curve of MgO at high pressure

Shell-model molecular dynamics method is used to study the melting temperatures of MgO at elevated temperatures and high pressures using interaction potentials. Equations of state for MgO simulated by molecular dynamics are in good agreement with available experimental data. The pressure dependence of the melting curve of MgO has been calculated. The surface melting and superheating are considered in the correction of experimental data and the calculated values, respectively. The results of corrections are compared with those of previous work. The corrected melting temperature of MgO is consistent with corrected experimental measurements. The melting temperature of MgO up to 140GPa is calculated.     

不同晶面银纳米晶高温熔化的各向异性

采用嵌入原子势, 使用分子动力学方法, 模拟研究了银纳米晶高温弛豫过程中的热稳定性和熔化机制, 并引入均方位移和稳定寿命来分析它的结构和形状的演化过程. 结果表明: 对于沿相互垂直{110}, {211}和{111}面切割形成的近正方体截面纳米晶, 高温弛豫熔化存在明显的各向异性行为; (112) 面热稳定性最低, 最易熔化, 其次是(110) 面, 热稳定性最高的是(111) 面, 最难熔化; 三个不同晶面的最外层和次外层原子的稳定寿命极短, 且三个不同晶面之间相差很小, 没有明显差异; 对于具有相同晶面指数的晶面, 第三层及其以内的稳定寿命较长, 且依次微量增长, 但不同晶面第三层及其以内的寿命相差明显.     

Molecular dynamics simulations of the melting of Al–Ni nanowires

Molecular dynamics (MD) simulations were performed to investigate the influence of nickel (Ni) composition and nanowire thickness on the thermal properties of Al-x%Ni (at%) nanowires using the embedded atom model (EAM) potential. The melting of the nanowire was characterised by studying the temperature dependence of the cohesive energy and mean square displacement. The effect of the nanowire thickness on the cohesive energy, melting temperature, heat capacity as well as latent heat was studied in canonical ensemble. Moreover, the crystal stability of Al, Al-20%Ni, Al-40%Ni, Al-60%Ni, Al-80%Ni, Al₃Ni, Ni₃Al and Ni nanowires was studied at different temperatures using mean square displacement and cohesive energy.     

Composition-dependent melting behaviour of NaxK55–x core–shell nanoalloys

Molecular dynamics simulations at constant temperature are performed to investigate melting-like transition in Na₁₃K₄₂, Na₁₉K₃₆ and Na₂₆K₂₉ nanoalloys using a second-moment-approximation tight-binding analytic potential to calculate the forces on the constituent atoms. A weighted histogram analysis method is employed to remove non-ergodicity issues due to the complex potential energy surface of these nanoalloys. The heat capacity shows three distinctive steps in melting for Na₁₃K₄₂, while Na₂₆K₂₉ and Na₁₉K₃₆ have two-step and one-step melting transition, respectively. The steepest descent method is used to quench the configurations in a given interval during the simulation and also study the isomerisation processes occurring at different temperatures. Analysing the configuration energies of quenched structures for the entire nanoalloy and the core atoms separately gives more details about the melting mechanism. The Lindemann parameter is also calculated at several temperatures during the simulation which shows a gradual increase for Na₁₃K₄₂ and Na₂₆K₂₉ while a sharp change is observed for Na₁₉K₃₆. These findings are in agreement with the multi-step nature of the phase transition in Na₁₃K₄₂ and Na₂₆K₂₉ and one-step melting of the Na₁₉K₃₆ magic composition.     

储氢笼型水合物生成促进机理的分子动力学模拟研究

用分子动力学(MD)模拟方法研究水合物法储氢的促进机理,系统研究纯H₂水合物、H₂+四氢呋喃(THF)水合物、H₂+四丁基溴化铵(TBAB)半笼型水合物和H₂+四异戊基溴化铵(TiAAB)半笼型水合物的微观结构及性质.模拟分析客体与笼子之间的稳定能ΔE_GH,得出水合物中大笼子对稳定水合物起到主要作用.THF进入大笼子能促进H₂水合物稳定,降低H₂水合物形成压力,模拟结果与实验一致.模拟对比不同客体在大笼子中的ΔE_GH值,得出从小到大的顺序依次为TiAAB,TBAB,THF,H₂.模拟结果表明半笼型水合物的稳定性比结构Ⅱ型水合物强,同时得出H₂+TiAAB半笼型水合物的结构最稳定.MD模拟为TiAAB成为一种水合物新型促进剂和新型储氢材料提供了理论依据.关键词：2笼型水合物')\" href=\"#\">H₂笼型水合物分子动力学模拟储氢半笼型水合物     

载能氢同位素原子与石墨(001)面碰撞的分子动力学研究

采用分子动力学方法研究了载能H同位素原子与石墨晶体碰撞的同位素效应. 碳氢系统的强共价键作用和石墨层间的弱van der Waals力分别用REBO和Ito半经验势函数来描述. 研究发现: 随着入射原子质量的增加, 上表面吸附几率和反射几率的峰值都会向高能区移动; 相比于H, ²H入射原子, ³H入射原子具有较高的吸附几率——包括上表面吸附和内部吸附; 穿透石墨晶体, ²H, ³H原子所需的能量较高; 原子质量和原子入射能量都会影响入射粒子与不同石墨层之间的能量传递过程. 这些结果对理解碳基材料的³H滞留机制有重要意义.     

Molecular dynamics simulation of sulphur nucleation in S–H2S system

The mechanism of sulphur nucleation in S–H₂S system is investigated by molecular dynamics simulation with the ReaxFF reactive force field. The results indicate that the nucleation of sulphur requires certain conditions. The nucleus of sulphur will form once the allotropes of sulphur dissolve from polysulphanes. Separate sulphur atoms aggregate into the cluster in the initial stage of nucleation according to the snowball effect. The cluster of nucleation is judged by the average distance of the neighbour sulphur atoms, which is identified as 2.8 Å through a parametric study. The sustainable process of nucleation depends on whether the cluster can overcome its critical state. The formation of the cluster may accelerate its own nucleation/coalescence and H₂S decomposition.     

Molecular dynamics simulations on the melting of gold nanoparticles

Molecular dynamics is employed to study the melting of bulk gold and gold nanoparticles. PCFF, Sutton-Chen and COMPASS force fields are adopted to study the melting point of bulk gold and we find out that the Sutton-Chen force field is the most accurate model in predicting the melting point of bulk gold. Consequently, the Sutton-Chen force field is applied to study the melting points of spherical gold nanoparticles with different diameters. Variations of diffusion coefficient, potential energy and translational order parameter with temperature are analyzed. The simulated melting points of gold nanoparticles are between 615～1115 K, which are much lower than that of bulk gold (1336 K). As the diameter of gold nanoparticle drops, the melting point also descends. The melting mechanism is also analyzed for gold nanoparticles.     

纳米团簇熔化过程的分子动力学模拟

本文采用分子动力学结合嵌入原子多体势,模拟了不同半径的Ni纳米团簇的升温熔化过程,研究团簇尺寸对熔点和表面能的影响.模拟结果表明:团簇的熔点显著低于体材料的熔点.团簇熔化的过程首先是在团簇的表面出现预熔,然后向团簇内部扩展,直到整个团簇完全熔为液态.在模拟的纳米尺度范围内,团簇的熔点与团簇尺寸基本成线性关系.团簇的表面能随着团簇尺寸的增大而减小,而且表面能均高于体材料的表面能.     

[110]Au纳米线在加温过程中结构与热稳定性的原子级模拟研究

采用分子动力学方法结合量子修正Sutton-Chen型多体力场,对[110]Au纳米线在升温过程中的结构与热稳定性进行了研究,并引入Lindemann指数和最小半径来研究它的熔化机理和形状演化.结果表明:纳米线在预熔之前,局部区域发生了由fcc到hcp的结构转变.纳米线的预熔首先出现表面上,然后向内部传播,最后才完全熔化为液态结构.纳米线在完全熔化后才开始出现径缩,并最终断裂成为球形纳米团簇.     

Pt-Au核-壳结构纳米粒子热稳定性的分子动力学研究

采用分子动力学方法结合嵌入原子势, 对Pt-Au核-壳纳米粒子的热稳定性进行了研究. 计算结果表明: Pt-Au纳米粒子的熔点明显高于Au纳米粒子而低于Pt纳米粒子. 通过计算Lindemann指数发现: 壳层中的Au首先熔化, 然后逐渐向内部扩展, 最终导致核中的Pt完全熔化; 熔化所经历的温度区间明显宽于单质纳米粒子, 而且该熔化过程呈现典型的两阶段熔化特征; 在两次熔化之间, 存在着固(核)液(壳)共存的结构.关键词：纳米粒子熔化分子动力学     

Au-Pd共晶纳米粒子熔化行为的分子动力学研究

采用分子动力学方法结合嵌入原子势, 对Au-Pd共晶纳米粒子的热稳定性进行了模拟研究. 计算结果表明: Au-Pd纳米粒子的熔点明显高于Au单质纳米粒子而低于Pd纳米粒子. 通过计算Lindemann指数发现Au-Pd共晶纳米粒子中的Au原子首先熔化, 然后带动Pd原子的熔化; 熔化所经历的温度区间明显要宽于单质纳米粒子.     

Recent advances on “ordered water monolayer that does not completely wet water” at room temperature

The molecular scales behavior of interfacial water at the solid/liquid interfaces is of a fundamental significance in a diverse set of technical and scientific contexts,ranging from the efficiency of oil mining to the activity of biological molecules.Recently,it has become recognized that,both the physical interactions and the surface morphology have significant impact on the behavior of interfacial water,including the water structures as well as the wetting properties of the surface.In this review,we summarize some of recent advances in the atom-level pictures of the interfacial water,which exhibits the ordered character on various solid surfaces at room or cryogenic temperature.Special focus has been devoted to the wetting phenomenon of"ordered water monolayer that does not completely wet water"and the underlying mechanism on model and some real solid surfaces at room temperature.The possible applications of this phenomenon are also discussed.